In order to deal with many forums related to a fourth generation mobile communication and a new technology, 3GPP establishing a technology standard of a third generation mobile communication system has started to conduct a study on LTE/SAE (Long Term Evolution/System Architecture Evolution) technology by the end of 2004 in a bid to optimize and enhance performance of 3GPP technologies.
The SAE proceeded centering on 3GPP SA WG2 is a study on a network technology having a purpose of determining a network structure in a manner of juggling an LTE job of 3GPP TSG RAN and the purpose of supporting mobility between heterogeneous networks. Currently, the SAE is one of important standardization issues of 3GPP. This is a job to develop a 3GPP system to a system supporting various radio access technologies based on an IP. The job has been progressed to achieve a target of an optimized packet-based system minimizing a transmission delay with a more enhanced data transmission capability.
An SAE upper level reference model defined by the 3GPP SA WG2 includes a non-roaming case and roaming cases of various scenarios. Detail contents may refer to 3GPP standard document TS 23.401 and TS 23.402. A diagram of a network structure in FIG. 1 corresponds to a simple reconstruction of the SAE upper level reference model.
FIG. 1 is a diagram of a structure of an evolved mobile communication network.
One of main characteristics of the network structure in FIG. 1 corresponds that the structure is based on a 2 Tier Model, i.e., an eNode B of Evolved UTRAN and a Gateway of a Core Network. Although it is not perfectly matched to each other, the eNode B may perform a function similar to the function of RNC of a Node B of a legacy UMTS system and the Gateway may perform a function similar to the function of SGSN/GGSN of a legacy system.
Another main characteristic of the network structure is that a Control Plane and a User Plane between an Access network and the Core Network are exchanged by an interface different from each other. In the legacy UMTS system, there exist one interface, i.e., Iu, between RNC and SGSN. On the other hand, since an MME (Mobility Management Entity) in charge of processing a control signal has a structure separated from the GW(Gateway), two types of interface, i.e., S1-MME and S1-U, can be used, respectively.
FIG. 2 is a diagram of an (e)Node B and a Home (e)Node B.
An attempt to increase cell capacity in order to support such a high-capacity service as multimedia content, streaming, and the like and a bidirectional service in the third generation or the fourth generation mobile communication system continues.
In particular, since various transmission techniques of high-capacity are required according to a development of a communication and dissemination of a multimedia technology, it is able to allocate more frequency resources to increase radio capacity. Yet, since the frequency resource is limited, there exist a limit for allocating the limited frequency resource to a plurality of users.
In order to increase the cell capacity, an approach of using a high frequency band and the approach of reducing a cell radius have been tried. If such a cell of a small radius as a pico cell and the like are applied, since it is able to use a frequency band higher than the frequency band used in a legacy cellular system, more information can be delivered. Yet, since more base stations are necessary to be installed in an identical area, cost may dramatically increase instead.
As mentioned in the foregoing description, recently, a femto base station such as the Home (e)Node B is proposed among the approaches of increasing the cell capacity by using a small cell.
The (e)Node B 20 depicted in FIG. 2 corresponds to a macro base station and the Home (e)Node B 30 may correspond to the femto base station. It is intended that the present specification is explained based on a terminology of 3GPP and the (e)Node B 20 is used when a Node B and an eNode B are mentioned together. And, the Home (e)Node B is used when a Home Node B and a Home eNode B are mentioned together.
Meanwhile, a cell of the Home (e)Node B 30 includes an open access mode, a closed access mode, and a hybrid access mode according to an access permit policy.
In case of the open access mode, the Home (e)Node B 30 cell provides a service to serviceable user equipments without a limit.
In case of the closed access mode, accessing the Home (e)Node B cell is allowed only for a user equipment allowed to the corresponding Home (e)Node B 30 cell.
Regarding the closed access mode, UMTS/EPS of 3GPP standard proposes to support the cell of the Home (e)Mode B 30 in a closed subscriber group (CSG) unit. In particular, one closed subscriber group (CSG) can be configured with at least one Home (e)Node B. Authority for use for the cell of the Home (e)Node B is provided to the user equipment as well in the closed subscriber group (CSG) unit. In this case, the user equipment can include at least one available closed subscriber group (CSG) and can possesses time information allowed according to each of the closed subscriber groups. This is called an allowed CSG list. The allowed CSG list is stored in the user equipment and such a network entity as MME, SGSN, MSC, HSS, HLR, and the like.
FIG. 3 is a diagram of an example of an operation mode of a Home (e)Node B.
The aforementioned and depicted femto base station, e.g., the Home (e)Node B 30 can operate in three modes, i.e., the open access mode of FIG. 3 (a), the closed access mode of FIG. 3 (b), and the hybrid access mode of FIG. 3 (c).
First of all, referring to FIG. 3 (a), an example of the open access mode is displayed. As defined in the foregoing description, the open access mode indicates that all user equipments are able to access without limit for accessing the cell of the Home (e)Node B 30. Hence, as depicted in FIG. 3 (a), access of a plurality of UEs 11/12/13 are all allowed.
Referring to FIG. 3 (b), an example of the closed access mode is displayed. The closed access mode indicates that the Home (e)Node B 30 operates as a closed subscriber group (CSG) cell. In other word, the Home (e)Node B 30 allows an access only for an allowed user equipment. The Home (e)Node Bs 30 have a CSG ID(s) capable of providing a service. Each user receives an approval of use according to the CSG.
Referring to FIG. 3 (c), an example of the hybrid access mode is displayed.
Although the hybrid access mode operates as a CSG cell providing a service to a closed subscriber group (CSG), the hybrid access mode allows a user equipment of a non-closed subscriber group to access. For instance, as depicted in FIG. 3 (c), although a first UE 11 is not a member of the CSG, the first UE can access the Home (e)Node B 30.